The preparation of cyclic diesters by thermolysis of linear polyesters in the presence of catalysts is disclosed in French Pat. No. 796,410. The catalysts employed are inorganic salts, e.g., chlorides, nitrates, carbonates, and oxides of magnesium, manganese, iron, cobalt, and tin. Attempted preparation of cyclic diesters of dodecanedioic acid in this fashion gives yields of less than 25%.
Improved yields are obtained by the method of Japanese Laid-Open application No. 4,826,790 and Japanese Published application No. 4,920,503, wherein linear polyesters of dodecanedioic acid and ethylene glycol are treated with lead nitrate or lead dioxide, respectively, at 260.degree.-280.degree. C. under reduced pressure. Crude yields of up to 88% of cyclo(ethylenedodecanedioate) are obtained. However, lead compounds utilized as the catalysts are present in the reaction products in considerable amounts, even after a fine-distillation step.
Because the cyclic esters, owing to their odor characteristics, are utilized primarily in the cosmetic industry as fixatives, e.g., in perfumes, soaps, or mouthwashes, the presence of lead-containing contaminants in the esters used for these purposes is prohibited for physiological reasons. Furthermore, problems are encountered in removal and/or dumping of lead-containing residue from the thermolysis.
Therefore, there is a continuing need for a process for producing cyclic esters of dodecanedioic acid which are free of toxic, lead-containing residues.